1. Field of the Invention
This invention relates to electric motors and synchronous generators. More particularly, it relates to a motor or generator that operates at a very high efficiency over a broad range of loads.
2. Description of the Prior Art
Single phase alternating current electric motors are typically used for low horse power applications. Their range may extend from a fractional horsepower up to about ten horsepower. Three phase motors are typically used when the horsepower requirements exceed ten horsepower.
U.S. Pat. No. 4,446,416A to Wanlass, granted May 1, 1984, entitled “Polyphase Electric Machine Having Controlled Magnetic Flux Density” discloses a stator core having main windings and additional control windings. The flux density is optimized in a polyphase machine by controlling the flux density in the stator core. More particularly, a main polyphase stator winding is wound on a magnetic core and includes a plurality of windings where each winding represents a single phase. Capacitors are connected in series to each of the windings. The capacitors reduce reactive power.
An additional motor winding technique is also disclosed in German patent application No. 2508374 to Wen, published Sep. 9, 1976 and entitled “Single Phase Induction Motor.” Wen discloses a single phase motor having two start windings to increase the start capacitor voltage. Wen also discloses a single phase induction motor having two sets of start windings to provide a better running power factor and an improved starting torque.
The Wanlass and the Wen motors, like all motors heretofore known, operate most efficiently at full load and are less efficient in low load conditions. Thus, a conventional motor might have a power factor greater than 0.90 during full load conditions and a power factor of 0.50 or less at low load.
A power company experiences the exact reverse percentage proportion of the power factor to supply energy to any electric motor. A motor running at 0.70 power factor uses thirty percent (30%) more amperage than one running at unity power factor (0.999 or 1.00). A generator supplying power will be overloaded by the supplement of amp demand and will simultaneously transfer that to the driver (diesel or turbine), that will need that much more energy to produce for the new demand. The new demand in kilowatts is Identical to the original demand. The only change is in the power factor. Accordingly, use of motors that cannot perform at a high power factor at all loads is contraindicated.
A motor that operates at a high power factor over all loads is therefore needed. However, the conventional wisdom has been for many decades that motors will always operate at reduced efficiency when the loads applied thereto are reduced because such lower efficiency at low loads is an inherent feature of motors. Power factors in the range of 0.90 and greater at low load conditions have been considered to be impossible to attain.
Any producer of electricity is penalized in its production when it supplies costumers that use poor power factor (P/F) standard motors. The penalty is even greater if such motors are often used at low duty cycle (from no load to seventy-five percent (75%) load) or if such motors are fed through V.F.D (Variable Frequency Drive). When a motor is reduced in speed by reducing the frequency it automatically drops in power factor.
For example: A motor (A) that pulls thirty (30) amps at four hundred sixty (460) volts at 0.88 power factor will consume 21.03 KW. (30 amps×460 volts×1.732×0.88 P/F).
Another motor (B) of the same H.P. running at an average P/F of 0.68, will also consume 21.03 KW. The amperage increases to 38.83 amps (38.83 amps×460 volts×1.732×0.68 P/F)
The KW consumed by motor (A) is identical to the KW consumed by motor (B). This means that to supply motor (B), a power company will have to produce 29.4% more amperage out of their generator than to supply motor (A). The generator that produces the electricity is typically driven by a diesel engine or a steam turbine. Current is the factor that loads and unloads generators, so the direct consequence of the above comparison of motors is that it will cost 29.4% more energy (diesel fuel, coal, and the like) to produce the same 21.03 KW for motor (B) than for motor (A).
It could be concluded that the owner of motor (B) should pay more for its 21.03 KW than the owner of motor (A). Alternatively, the owner of motor (B) should be required to convert said low power factor motor to a high power factor motor.
What is needed, then, is an improvement in motors that increases the power factor of a motor so that less energy is required to perform a given task vis a vis the energy required by conventional, low power factor motors. For example, if the power factor could be increased to 0.98, the current would drop to 26.93 amps. Multiplying that amperage by 460 volts and 1.732 and 0.98 P/F yields 21.03 KW. Note that the current drawn is 38.83 amps with a P/F of 0.68, 30.0 amps with a P/F of 0.88, and 26.93 amps with a P/F of 0.98.
However, in view of the prior art considered as a whole at the time the present invention was made, it was not obvious to those of ordinary skill in the art of motors how to substantially increase the power factor of motors.